enhance(#1962): harden regression tests (PBT shrinking + oracle classification + boundaries) (#2409)

* test(#1962): add failing-first repro-hardening contract tests

Epic #1957 Phase 3A. Source-text-is-the-product contract tests: PBT shrinking
(fast-check/Hypothesis, minimized seed, manual-minimization degradation), the
four oracle types (specified/derived/metamorphic/implicit with implicit flagged
weakest), boundary neighbors (off-by-one/min-max/empty-singleton tied to the
equivalence class), oracle_type in DEBUG Resolution, and the Phase 1A tie-in
(minimized seed + real oracle => the mutation guardrail bites).

Failing-first: reference, agent cross-refs, and template field do not yet exist.

* feat(#1962): harden regression tests (PBT shrinking + oracle classification + boundaries)

Epic #1957 Phase 3A. Extends Minimal Reproduction (shrinking) and Test-First
Debugging (oracle classification + boundary neighbors):
- Shrinking: wrap an input-space failing input in a property (fast-check JS/TS,
  Hypothesis Python) and store the MINIMIZED counterexample as the regression
  seed; degrade to manual minimization when no PBT framework is present.
- Oracle classification: state specified / derived (contract/model) /
  metamorphic / implicit (crash, weakest) before writing the assertion; record
  under Resolution.oracle_type; never default to implicit silently.
- Boundary neighbors: off-by-one, min/max, empty/singleton around the fixed
  defect's equivalence class.

Together they turn the regression test into a root-cause check — what the Phase
1A mutation guardrail needs to bite. Full rules extracted to gsd-core/references/
debugger-repro-hardening.md. INVENTORY + manifest + agent-size baseline +
install-parity goldens + AGENTS.md + DEBUG template updated.

* fix(#1962): address orthogonal review (bounding, provenance, oracle scope, sufficient-triple)

- HIGH: added a 'Bound the property/shrink run' section (60s timeout, degrade-
  to-manual on timeout, do-not-raise-default-run-limits, argv-not-shell) —
  the gauntlet violation the sibling references already honored.
- Medium: test-provenance caveat (the failing input often comes from the bug
  report — author the generator from a sanitized description, cross-ref
  debugger-fix-acceptance.md).
- Medium: oracle scope note — the 4 types cover deterministic bugs; non-
  deterministic failures re-route to stability-stress per bug-taxonomy.
- Medium: Phase 1A tie-in corrected — seed+oracle is necessary not sufficient;
  boundary neighbors close the adjacent-input escape; the sufficient triple is
  seed+oracle+neighbors.
- Low: preserve the original noisy repro as a secondary reference; operationalize
  'equivalence class' (the predicate the fix draws). Nit: degradation reworded.

* chore(#1962): backfill changeset pr number (PR #2409)

---------

Co-authored-by: sim <sim@local>

tests/fixtures/install-tree/claude.json

@@ -63,6 +63,7 @@
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
   "gsd-core/references/debugger-rca-branching.md",
+  "gsd-core/references/debugger-repro-hardening.md",
   "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",